Mounting table and plasma processing apparatus

ABSTRACT

A mounting table, to which a voltage is applied, includes an electrostatic chuck having a mounting surface for mounting a target object and a rear surface opposite to the mounting surface, the electrostatic chuck having a first through-hole formed in the mounting surface; a base, which is in contact with the rear surface of the electrostatic chuck, having a second through-hole communicating with the first through-hole; a cylindrical spacer inserted in the second through-hole; and a pin accommodated in the first through-hole and the spacer. Gaps are formed between the pin and inner walls of the first through-hole and the spacer, and the gap between the first through-hole and the pin is greater than the gap between the spacer and the pin.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2016-191707 filed on Sep. 29, 2016, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The disclosure relates to a mounting table and a plasma processingapparatus.

BACKGROUND OF THE INVENTION

Japanese Patent Application Publication No. 2014-143244 disclosestherein a plasma processing apparatus including a processing chambercapable of defining a vacuum space, a mounting table which mountsthereon a target object and serves as a lower electrode in theprocessing chamber, and an upper electrode provided to face the mountingtable. In the plasma processing apparatus disclosed in Japanese PatentApplication Publication No. 2014-143244, plasma processing is performedon the target object such as a wafer or the like which is mounted on themounting table by applying a high frequency power between the mountingtable serving as the lower electrode and the upper electrode.

Further, the plasma processing apparatus disclosed in Japanese PatentApplication Publication No. 2014-143244 includes a plurality of lifterpins for raising the target object from the mounting table. The lifterpins can protrude and retract with respect to a surface of the mountingtable. The mounting table has holes for accommodating the lifter pins.The plasma processing apparatus disclosed in Japanese Patent ApplicationPublication No. 2014-143244 has a gas hole for supplying a heat transfergas such as He gas or the like to a space between a backside of thetarget object and a top surface of the electrostatic chuck.

The plasma processing apparatus disclosed in Japanese Patent ApplicationPublication No. 2014-143244 has the lifter pins having inverted taperedupper end portions and pin through-holes having tapered upper endportions to prevent discharge occurrence between the target object andthe mounting table. The upper end portions of the lifter pins arebrought into surface contact with the upper end portions of the pinthrough-holes when the lifter pins are accommodated in the pinthrough-holes.

However, the configuration disclosed in Japanese Patent ApplicationPublication No. 2014-143244 needs to be improved to prevent dischargefrom occurring at the gas hole. Therefore, in this technical field,there are required a mounting table capable of preventing abnormaldischarge and a plasma processing apparatus including the mountingtable.

SUMMARY OF THE INVENTION

In accordance with an aspect, there is provided a mounting table towhich a voltage can be applied. The mounting table includes: anelectrostatic chuck, a base, a spacer and a pin. The electrostatic chuckhas a mounting surface for mounting a target object and a rear surfaceopposite to the mounting surface, and a first through-hole is formed inthe mounting surface. The base is in contact with the rear surface ofthe electrostatic chuck and has a second through-hole communicating withthe first through-hole. The spacer has a cylindrical shape, and isinserted in the second through-hole. The pin is accommodated in thefirst through-hole and the spacer. Gaps are formed between the pin andinner walls of the first through-hole and the spacer, and the gapbetween the first through-hole and the pin is greater than the gapbetween the spacer and the pin.

In the mounting table, the pin is accommodated in the first through-holeformed in the mounting surface and the spacer inserted in the secondthrough-hole communicating with the first through-hole. Therefore, thespace of the hole formed in the mounting table can be reduced not toprovide a space for acceleration of electrons. Accordingly, it ispossible to prevent discharge occurrence at the first through-hole andthe spacer. Further, the discharge can be prevented withoutdeteriorating the gas supply function because the gaps are formedbetween the pin and the inner walls of the first through-hole and thespacer. Moreover, when the electrostatic chuck and the base are formedof different materials, the contact point between the first thorugh-holeand the spacer may be deviated due to the difference between the thermalexpansion coefficients. In the mounting table described above, the gapbetween the pin and the first thorugh-hole is greater than the gapbetween the pin and the spacer. Accordingly, even when the electrostaticchuck and the base are formed of different materials, it is possible toavoid the damage of the pin inserted in the first through-hole and thespacer. In addition, the present inventors have found that abnormaldischarge can be effectively prevented when the space in the base isreduced compared with when the space in the electrostatic chuck isreduced. That is, by allowing the gap between the pin and the firstthorugh-hole to have the space enough to avoid the damage of the pin,the abnormal discharge can be effectively prevented while avoidingdamage of the pin.

In accordance with another aspect, there is provided a mounting table towhich a voltage can be applicaed. The mounting table includes: anelectrostatic chuck, a base and a pin. The electrostatic chuck has amounting surface for mounting a target object and a rear surfaceopposite to the mounting surface, and a first through-hole is formed inthe mounting surface. The base is in contact with the rear surface ofthe electrostatic chuck, and has a second through-hole communicatingwith the first through-hole. The pin is accommodated in the firstthrough-hole and the second through-hole. Gaps are formed between thepin and inner walls of the first through-hole and the secondthrough-hole, and the gap between the first through-hole and the pin isgreater than the gap between the second through-hole and the pin.

In such a mounting table, the pin is accommodated in the firstthrough-hole formed in the mounting surface and the second through-holecommunicating with the first through-hole. Therefore, the space of thehole formed in the mounting table can be reduced not to provide a spacefor acceleration of electrons. Accordingly, it is possible to preventdischarge occurrence at the first through-hole and the secondthrough-hole. Further, the discharge can be prevented withoutdeteriorating the gas supply function because the gaps are formedbetween the pin and the inner walls of the first through-hole and thesecond through-hole. Moreover, when the electrostatic chuck and the baseare formed of different materials, the contact point between the firstthorugh-hole and the second through-hole may be deviated due to thedifference between the thermal expansion coefficients. In the mountingtable described above, the gap between the pin and the firstthorugh-hole is greater than the gap between the pin and the secondthrough-hole. Accordingly, even when the electrostatic chuck and thebase are formed of different materials, it is possible to avoid thedamage of the pin inserted in the first through-hole and the secondthrough-hole. In addition, the present inventors have found thatabnormal discharge can be effectively prevented when the space in thebase is reduced compared with when the space in the electrostatic chuckis reduced. That is, by allowing the gap between the pin and the firstthorugh-hole to have the space enough to avoid the damage of the pin,the abnormal discharge can be effectively prevented while avoidingdamage of the pin.

In accordance with still another aspect, there is provided a plasmaprocessing apparatus including: a processing chamber, a gas supply unitand a mounting table. The processing chamber defines a processing spacewhere a plasma is generated. The gas supply unit is configured to supplya processing gas into the processing space. The mounting table isprovided in the processing space and configured to mount thereon atarget object. The mounting table includes an electrostatic chuck, abase, a spacer and a pin. The electrostatic chuck has a mounting surfacefor mounting a target object and a rear surface opposite to the mountingsurface, and a first through-hole is formed in the mounting surface. Thebase is in contact with the rear surface of the electrostatic chuck andhas a second through-hole communicating with the first through-hole. Thespacer has a cylindrical shape, and is inserted in the secondthrough-hole. The pin is accommodated in the first through-hole and thespacer. Gaps are formed between the pin and inner walls of the firstthrough-hole and the spacer, and the gap between the first through-holeand the pin is greater than the gap between the spacer and the pin.

In accordance with still another aspect, there is provided a plasmaprocessing apparatus including: a processing chamber, a gas supply unitand a mounting table. The processing chamber defines a processing spacewhere a plasma is generated. The gas supply unit is configured to supplya processing gas into the processing space. The mounting table isprovided in the processing space and configured to mount thereon atarget object. The mounting table includes an electrostatic chuck, abase and a pin. The electrostatic chuck has a mounting surface formounting a target object and a rear surface opposite to the mountingsurface, and a first through-hole is formed in the mounting surface. Thebase is in contact with the rear surface of the electrostatic chuck, andhas a second through-hole communicating with the first through-hole. Thepin is accommodated in the first through-hole and the secondthrough-hole. Gaps are formed between the pin and inner walls of thefirst through-hole and the second through-hole, and the gap between thefirst through-hole and the pin is greater than the gap between thesecond through-hole and the pin.

In accordance with various aspects and embodiments of the presentdisclosure, the mounting table and the plasma processing apparatusincluding the mounting table are capable of preventing abnormaldischarge.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the disclosure will become apparent from thefollowing description of embodiments, given in conjunction with theaccompanying drawings, in which:

FIG. 1 is a schematic cross sectional view showing a configuration of aplasma processing apparatus according to a first embodiment;

FIGS. 2 and 3 are schematic cross sectional views showing a mountingtable in the plasma processing apparatus shown in FIG. 1;

FIG. 4 is a schematic cross sectional view showing a configuration of agas hole in the mounting table shown in FIGS. 2 and 3;

FIG. 5 explains positional relation of components defining the gas holeshown in FIG. 4;

FIGS. 6A to 6F explain abnormal discharge;

FIG. 7 is a schematic cross sectional view showing a configuration of agas hole according to a second embodiment; and

FIG. 8 is a table showing occurrence/non-occurrence of discharge in testexamples and a comparative example.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments will be described in detail with reference tothe accompanying drawings. Like reference numerals will be used for likeor corresponding parts throughout the drawings. Terms “upper” and“lower” are used based on illustrated states, for convenience.

First Embodiment

FIG. 1 is a schematic cross sectional view showing a configuration of aplasma processing apparatus according to a first embodiment. The plasmaprocessing apparatus includes a processing chamber 1 that is airtightlysealed and electrically connected to a ground potential. The processingchamber 1 is formed in a cylindrical shape and made of, e.g., aluminumor the like. The processing chamber 1 defines a processing space where aplasma is generated. A mounting table 2 for horizontally supporting asemiconductor wafer (hereinafter, simply referred to as “wafer”) that isa target object is provided in the processing chamber 1. The mountingtable 2 includes a base 2 a and an electrostatic chuck 6. The base 2 ais made of a conductive metal, e.g., aluminum or the like, and serves asa lower electrode. The electrostatic chuck 6 has a function ofattracting and holding the wafer W. The mounting table 2 is supported bya conductive support 4 through an insulating plate 3. A focus ring 5made of, e.g., single crystalline silicon, is provided on an outerperiphery of the mounting table 2. A cylindrical inner wall member 3 amade of, e.g., quartz or the like, surrounds outer peripheries of themounting table 2 and the support 4.

The base 2 a is connected to a first RF power supply 10 a via a firstmatching unit 11 a and connected to a second

RF power supply 10 b via a second matching unit 11 b. The first RF powersupply 10 a is used for plasma generation and configured to supply ahigh frequency power having a predetermined high frequency to the base 2a of the mounting table 2. The second RF power 10 b is used for ionattraction (bias) and configured to supply a high frequency power havinga predetermined frequency lower than that of the first RF power supply10 a to the base 2 a of the mounting table 2. In this manner, a voltagecan be applied to the mounting table 2. A shower head 16 serving as anupper electrode is provided above the mounting table 2 to face themounting table 2. The shower head 16 and the mounting table function asa pair of electrodes (upper electrode and lower electrode).

The electrostatic chuck 6 has a configuration in which an electrode 6 ais buried in an insulator 6 b. A DC power supply 12 is connected to theelectrode 6 a. By applying a DC voltage from the DC power supply 12 tothe electrode 6 a, the wafer W is attracted by a Coulomb force. Theinsulator 6 b is made of, e.g., ceramic or the like.

A coolant flow path 2 d is formed in the mounting table 2. A coolantinlet line 2 b and a coolant outlet line 2 c are connected to thecoolant flow path 2 d. By circulating a coolant, e.g., cooling water,through the coolant flow path 2 d, the mounting table 2 can becontrolled to a predetermined temperature. A gas supply line 30 forsupplying a cold heat transfer gas (backside gas) such as He gas or thelike to the backside of the wafer W is formed through the mounting table2 and the like. The gas supply line 30 is connected to a gas supplysource (not shown). With this configuration, the wafer W attracted andheld on the top surface of the mounting table 2 by the electrostaticchuck 6 is controlled to a predetermined temperature. A structure of thegas supply line 30 will be described later.

The mounting table 2 is provided with a plurality of, e.g., three pinthrough-holes 200 (only one shown in FIG. 1). Lifter pins 61 areinserted into the respective pin through-holes 200. The lifter pins 61are connected to a driving unit 62 and vertically moved by the drivingunit 62. A structure of the pin through-holes 200 will be describedlater.

The shower head 16 is provided at a ceiling wall of the processingchamber 1. The shower head 16 includes a main body 16 a and an upperceiling plate 16 b serving as an electrode plate. The shower head 16 issupported at an upper portion of the processing chamber 1 through aninsulating member 95. The main body 16 a is made of a conductivematerial, e.g., aluminum having an anodically oxidized surface anddetachably holds the upper ceiling plate 16 b therebelow.

A gas diffusion space 16 c is provided in the main body 16 a. Aplurality of gas through-holes 16 d is formed at a bottom portion of themain body 16 a and positioned below the gas diffusion space 16 c. Gasinjection holes 16 e are formed through the upper ceiling plate 16 b ina thickness direction thereof and overlapped with the gas through-holes16 d. With this configuration, a processing gas supplied into the gasdiffusion space 16 c is distributed and supplied in a shower shape intothe processing chamber 1 through the gas through-holes 16 d and the gasinjection holes 16 e.

A gas inlet port 16 g for introducing the processing gas into the gasdiffusion space 16 c is formed in the main body 16 a. One end of a gassupply line 15 a is connected to the gas inlet port 16 g. The other endof the gas supply line 15 a is connected to a processing gas supplysource (gas supply unit) 15 for supplying a processing gas. A mass flowcontroller (MFC) 15 b and an opening/closing valve V2 are installed inthe gas supply line 15 a in that order from an upstream side. Theprocessing gas for plasma etching is supplied from the processing gassupply source 15 into the gas diffusion space 16 c through the gassupply line 15 a and then distributed and supplied in a shower shapefrom the gas diffusion space 16 c into the processing chamber 1 throughthe gas through-holes 16 d and the gas injection holes 16 e.

A variable DC power supply 72 is electrically connected to the showerhead 16 serving as the upper electrode via a low pass filter (LPF) 71. Apower supply of the variable DC power supply 72 is on-off controlled byan on/off switch 73. Current/voltage of the variable DC power supply 72and on/off of the on/off switch 73 are controlled by a control unit 90to be described later. As will be described later, when a plasma isgenerated in the processing space by applying the high frequency powerfrom the first and the second RF power supply 10 a and 10 b to themounting table 2, the on/off switch 72 is turned on by the control unit90 and a predetermined DC voltage is applied to the shower head 16serving as the upper electrode, if necessary.

A cylindrical ground conductor 1 a extends upward from a sidewall of theprocessing chamber 1 to a position higher than a height of the showerhead 16. The cylindrical ground conductor 1 a has a ceiling wall at thetop thereof.

A gas exhaust port 81 is formed at a bottom portion of the processingchamber 1. A first gas exhaust unit 83 is connected to the gas exhaustport 81 via a gas exhaust line 82. The first gas exhaust unit 83 has avacuum pump. By operating the vacuum pump, a pressure in the processingchamber 1 can be decreased to a predetermined vacuum level. Aloading/unloading port 84 for the wafer W and a gate valve foropening/closing the loading/unloading port 84 are provided at a sidewallof the processing chamber 1.

A deposition shield 86 is provided along an inner wall surface of theprocessing chamber 1. The deposition shield 86 prevents etchingby-products (deposits) from being attached to the processing chamber 1.A conductive member (GND block) 89 is provided at a portion of thedeposition shield 86 at the substantially same height as the height ofthe wafer W. The conductive member 89 is connected such that a potentialwith respect to the ground can be controlled. Due to the presence of theconductive member 89, abnormal discharge is prevented. A depositionshield 87 extending along the inner wall member 3 a is provided at alower side of the deposition shield 86. The deposition shields 86 and 87are detachably provided.

The operation of the plasma processing apparatus configured as describedabove is integrally controlled by the control unit 90. The control unit90 includes a process controller 91 having a CPU, a user interface 92,and a storage unit 93.

The user interface 92 includes a keyboard for a process manager to inputcommands to operate the plasma processing apparatus, a display forvisualizing an operational status of the plasma processing apparatus,and the like.

The storage unit 93 stores therein recipes including a control program(software), processing condition data and the like for realizing variousprocesses performed by the plasma processing apparatus under the controlof the process controller 91. If necessary, any recipe is retrieved fromthe storage unit 93 in response to a command from the user interface 92or the like and executed by the process controller 91. Accordingly, adesired process in the plasma processing apparatus is performed underthe control of the process controller 91. Further, the recipes includingthe control program, the processing condition data and the like can bestored in a computer-readable storage medium (e.g., a hard disk, a CD, aflexible disk, a semiconductor memory, or the like) or can betransmitted, when needed, from another apparatus, via, e.g., a dedicatedline, and used on-line.

Hereinafter, a main configuration of the mounting table 2 will bedescribed with reference to FIGS. 2 and 3. FIGS. 2 and 3 are schematiccross sectional views of the mounting table 2 in the plasma processingapparatus shown in FIG. 1. FIG. 2 shows a case in which the wafer W israised and supported by the lifter pins 61. FIG. 3 shows a case in whichthe wafer W is supported on the electrostatic chuck 6 by lowering thelifter pins 61. As described above, the mounting table 2 includes thebase 2 a and the electrostatic chuck 6, and the lifter pins 61 can beinserted from a lower portion of the base 2 a to protrude beyond theelectrostatic chuck 6.

The electrostatic chuck 6 is formed in a disc shape and has a mountingsurface 21 for mounting the wafer W thereon and a rear surface 22opposite to the mounting surface 21. The mounting surface 21 has acircular shape and supports the disc-shaped wafer W while being incontact with the backside of the wafer W. The base 2 a is in contactwith the rear surface 22 of the electrostatic chuck 6. The electrostaticchuck 6 can be made to be in contact with the surface of the base 2 a byusing an adhesive.

An end portion (gas hole) of the gas supply line 30 is formed at themounting surface 21. The gas supply line 30 supplies He gas for coolingor the like. The end portion of the gas supply line 30 is formed by afirst through-hole 17 and a second through-hole 18. The firstthrough-hole 17 extends from the rear surface 22 to the mounting surface21 of the electrostatic chuck 6. In other words, the electrostatic chuck6 defines an inner wall of the first through-hole 17. The secondthrough-hole 18 extends from a rear surface of the base 2 a to a contactsurface with the electrostatic chuck 6. In other words, the base 2 adefines an inner wall of the second through-hole 18. A diameter of thesecond through-hole 18 is greater than that of the first through-hole17. The electrostatic chuck 6 and the base 2 a are arranged such thatthe first through-hole 17 and the second through-hole 18 communicatewith each other. A gas spacer 204 is provided at the gas supply line 30.

The gas spacer 204 is made of an insulator, e.g., ceramic or the like,and has a cylindrical shape. The gas spacer 204 has an outer diameterthat is substantially equal to the diameter of the second through-hole18 so that the gas spacer 204 can be in contact with the base 2 a insidethe second through-hole 18 and insertion-fitted into the secondthrough-hole 16 from a bottom surface toward a top surface of the base 2a. The gas spacer 204 has an inner diameter smaller than the diameter ofthe first through-hole 17.

A pin 31 is accommodated in the gas hole. The pin 31 is accommodated inthe first through-hole 17 and the gas spacer 204. An outer diameter ofthe pin 31 is smaller than the inner diameter of the gas spacer 204 andthe inner diameter of the first through-hole 17. In other words, the gasspacer 204 has an inner diameter that is smaller than the diameter ofthe first through-hole 17 and greater than the outer diameter of the pin31. The pin 31 may be made of an insulator, e.g., ceramic or the like.

The pin through-holes 200 for accommodating the respective lifter pins61 are formed in the mounting surface 21. The first through-hole 17 andthe second through-hole 18 form the pin through-hole 200. As describedabove, the first through-hole 17 is formed at the electrostatic chuck 6and the second through-hole 18 is formed at the base 2 a. The firstthrough-hole 17 forming the pin through-hole 200 has a diameter slightlygreater than the outer diameter of the lifter pin 61 (by, e.g., 0.1 mmto 0.5 mm) and, thus, the lifter pin 61 can be accommodated therein. Thediameter of the second through-hole is greater than, e.g., the diameterof the first through-hole. A pin spacer 203 is provided between theinner wall of the second through-hole 18 and the lifter pin 61.

The pin spacer 203 is provided in the second through-hole 18 forming thepin through-hole 200. The pin spacer 203 is made of an insulator, e.g.,ceramic or the like, and has a cylindrical shape. The pin spacer 203 hasan outer diameter that is substantially equal to the diameter of thesecond through-hole 18 so that the pin spacer 203 can be in contact withthe base 2 a inside the second through-hole 18 and is insertion-fittedinto the second through-hole 18 from the bottom surface toward the topsurface of the base 2 a. The pin spacer 203 has an inner diameter thatis smaller than the diameter of the first through-hole 17 and greaterthan the outer diameter of the lifter pin 61.

The lifter pin 61 includes a pin-shaped pin main body 61 a made ofinsulating ceramic or resin and an upper end portion 61 b. The pin mainbody 61 a is formed in a cylindrical shape and has an outer diameter of,e.g., a few mm. The upper end portion 61 b is formed by chamfering thepin main body 61 a and has a spherical surface. The spherical surfacehas, e.g., a considerably large curvature, and the entire pin upper endportion 61 b of the lifter pin 61 is positioned close to the backside ofthe wafer W. The lifter pin 61 can vertically move through the pinthrough-hole 200 to protrude beyond and retreat below the mountingsurface 21 of the mounting table 2 by the driving unit 62 shown inFIG. 1. The driving unit 62 adjusts a height of a stop position of thelifter pin 76 such that the pin upper end portion 61 b of the lifter pin61 is positioned right below the backside of the wafer W when the lifterpin 61 is accommodated.

As shown in FIG. 2, when the lifter pin 61 is raised, a part of the pinmain body 61 a and the pin upper end portion 61 b protrude beyond themounting surface 21 of the mounting table 2 and the wafer W is supportedabove the mounting table 2. As shown in FIG. 3, when the lifter pin 61is lowered, the pin main body 61 a is accommodated in the pinthrough-hole 200 and the wafer W is mounted on the mounting table 21. Inthis manner, the lifter pin 61 vertically moves the wafer W.

FIG. 4 is a schematic cross sectional view showing a configuration ofthe gas hole in the mounting table shown in FIGS. 2 and 3. As shown inFIG. 4, a gap CL1 is formed between a side portion of the pin 31 and thefirst through-hole 17; a gap CL2 is formed between the side portion ofthe pin 31 and an inner wall 204 a of the spacer 204; and a gap CL3 isformed between the upper end of the pin 31 and the backside of the waferW. The gap CL1 is greater than the gap CL2.

FIG. 5 explains positional relation of components defining the gas holeof FIG. 4. As shown in FIG. 5, on the assumption that: the center of themounting surface 21 is P1; the center of the gas hole is P2; a distancefrom the center P1 of the mounting surface 21 to the center of the firstthrough-hole 17 (the center P2 of the gas hole) is R; a diameter of thepin 31 is D; a diameter of the first through-hole 17 is d1; a diameterof the second through-hole 18 is d2; a length of the gap CL1 in thefirst through-hole 17 is g1; a length of the gap in the secondthrough-hole 18 is g2; a thermal expansion coefficient of the base 2 ais α1; a thermal expansion coefficient of the electrostatic chuck 6 isα2; and a difference between a target temperature and a referencetemperature that is a temperature measured when the first and the secondthrough-hole 17 and 18 are coaxially disposed is ΔT, the length g1 ofthe gap CL1 in the first through-hole satisfies the following relation.

g1≥(2·(R·(α1−α2)·ΔT+D)−d2−D)/2

In FIG. 5, the gas spacer 204 is omitted. When the gas spacer 204 isprovided, the length g2 of the gap CL2 in the second through-hole 18corresponds to a distance between an inner wall of the gas spacer 204and the side portion of the pin 31. When the gas spacer 204 is notprovided, the length g2 of the gap CL2 in the second through-hole 18corresponds to a distance between the inner wall of the secondthrough-hole 18 and the side portion of the pin 31.

Next, the effect of the gaps CL1 and CL2 on abnormal discharge will beexplained. In order to prevent the abnormal discharge, it is importantto remove a space where electrons are accelerated and, thus, it isrequired to minimize both of the gaps CL1 and CL2. However, when both ofthe gaps CL1 and CL2 are decreased, the pin 31 may be damaged due to thedifference between thermal expansion coefficients of the base 2 a andthe electrostatic chuck 6. Therefore, in order to ensure a space, one ofthe gaps CL1 and CL2 needs to be set greater than the other.

FIGS. 6A to 6F explain the abnormal discharge. FIGS. 6A to 6C show acase in which the gap CL2 is greater than the gap CL1. FIGS. 6D to 6Fshow a case in which the gap CL1 is greater than the gap CL2. The gasspacer 204 is omitted in FIGS. 6A to 6F.

First, the case in which the gap CL2 is greater than the gap CL1 will bedescribed. As shown in FIG. 6A, when the voltage is applied to themounting table, an electric field is generated between a side portion 2ae of the base 2 a (side portion of the gas spacer 204 when the gasspacer 204 is provided) which defines the gap CL2 and a correspondingportion WE in the backside of the wafer W. At this time, a space that isenough for acceleration of electrons exists, so that micro-hollowcathode discharge PL1 occurs in the gap CL2. Then, as shown in FIG. 6B,electrons are supplied from the gap CL2 to the gap CL1. Accordingly, asshown in FIG. 6C, glow discharge occurs at the backside of the wafer W.In other words, it is considered that when the gap CL2 is greater,abnormal discharge is caused by the micro-hollow cathode discharge.

Next, the case in which the gap CL1 is greater than the gap CL2 will bedescribed. As shown in FIG. 6D, when the voltage is applied to themounting table, an electric field is generated between the side portion2 ae of the base 2 a (side portion of the gas spacer 204 when the gasspacer 204 is provided) which defines the gap CL2 and the correspondingportion WE in the backside of the wafer W. At this time, a space that isenough for acceleration of electrons does not exist, so that themicro-hollow cathode discharge PL1 does not occur in the gap CL2.Therefore, as shown in FIGS. 6E and 6F, glow discharge does not occur atthe backside of the wafer W. In other words, it is considered that whenthe gap CL2 is smaller, the occurrence of abnormal discharge caused bythe micro-hollow cathode discharge can be suppressed.

As described above, in the mounting table 2 and the plasma processingapparatus according to the first embodiment, the pin 31 is accommodatedin the first through-hole 17 formed at the mounting surface 21 and thegas spacer 204 inserted in the second through-hole 18 communicating withthe first through-hole 17. Therefore, the space of the hole formed inthe mounting table 2 can be reduced not to provide a space foracceleration of electrons. Accordingly, it is possible to preventdischarge occurrence at the first through-hole 17 and the gas spacer204. Further, the discharge can be prevented without deteriorating thegas supply function because the gaps are formed between the pin 31 andthe inner walls of the first through-hole 17 and the gas spacer 204.When reducing either one of the gap CL1 or CL2 since it is not possibleto reduce both of the gaps CL1 and CL2, the gap CL2 that is effective insuppressing the occurrence of abnormal discharge is reduced.Accordingly, the abnormal discharge can be effectively prevented whileavoiding damage of the pin 31.

Second Embodiment

A mounting table and a plasma processing apparatus according to a secondembodiment are the same as the mounting table and the plasma processingapparatus according to the first embodiment except that the pin spacer203 and the gas spacer 204 are not provided. Hereinafter, redundantdescription will be omitted and differences will be described mainly.

FIG. 7 is a schematic cross sectional view showing a configuration ofthe gas hole in the mounting table. As shown in FIG. 7, a gap CL1 isformed between the side portion of the pin 31 and the first through-hole17; a gap CL2 is formed between the side portion of the pin 31 and thesecond through-hole 18; and a gap CL3 is formed between the upper end ofthe pin 31 and the backside of the wafer W. The gap CL1 is greater thanthe gap CL2. The other configurations of the mounting table are the sameas those in the first embodiment.

In the mounting table 2 and the plasma processing apparatus according tothe second embodiment, the pin 31 is accommodated in the firstthrough-hole 17 formed in the mounting surface 21 and the secondthrough-hole 18 communicating with the first through-hole 17. Therefore,the space of the hole formed in the mounting table 2 can be reduced notto provide a space for acceleration of electrons. Accordingly, it ispossible to prevent the discharge occurrence at the first and the secondthrough-hole 17 and 18. Further, the discharge can be prevented withoutdeteriorating the gas supply function because the gaps are formedbetween the pin 31 and the inner walls of the first and the secondthrough-hole 17 and 18. When reducing either one of the gap CL1 or CL2since it is not possible to reduce both of the gaps CL1 and CL2, the gapCL2 that is effective in suppressing the occurrence of abnormaldischarge is reduced. Accordingly, the abnormal discharge can beeffectively prevented while avoiding damage of the pin 31.

While the embodiments have been described, the present disclosure is notlimited to the above-described embodiments and may be variously modifiedor changed within the scope of the present disclosure as defined in theclaims.

For example, in FIG. 4, the gap CL1 is made to be greater than the gapCL2 by setting the diameter of the first through-hole 17 to be greaterthan the inner diameter of the gas spacer 204. However, the gap CL1 maybe made to be greater than the gap CL2 by changing the shape of the pin31. In the same manner, in FIG. 7, the gap CL1 is made to be greaterthan the gap CL2 by setting the diameter of the first through-hole 17 tobe greater than the inner diameter of the gas spacer 204. However, thegap CL1 may be made to be greater than the gap CL2 by changing the shapeof the pin 31.

In the above-described embodiments, the pin 31 may be a lifter pin.

In the first and the second embodiment, the plasma processing apparatusmay use a plasma generated by a radial line slot antenna.

TEST EXAMPLES

Hereinafter, test examples and a comparative example that have beenperformed by the present inventors to explain the above effects will bedescribed.

Test Example 1

The plasma processing apparatus according to the first embodiment wasused. The wafer W was mounted on the mounting table 2. A plasma wasgenerated by applying a voltage to the mounting table 2 (first RF powersupply 10 a: 2700 W, second RF power supply 10 b: 19000 W, pressure: 30Torr (3.9×10³ Pa)). He gas was used as a heat transfer gas. The gap CL1was set to 0.15 mm. The gap CL2 was set to 0.05 mm. The gap CL3 was setto 0.2 mm. The plasma processing was performed for a predeterminedperiod of time. Then, it was checked whether or not a discharge mark wasformed on the backside of the wafer W.

Test Example 2

The gap CL3 was set to 0.3 mm. The other conditions were the same asthose in the test example 1.

Comparative Example

The plasma processing apparatus according to the first embodiment wasused. A wafer W was mounted on the mounting table 2. A plasma wasgenerated by applying a voltage to the mounting table 2. The gap CL1 wasset to 0.035 mm. The gap CL2 was set to 0.2 mm. The gap CL3 was set tosubstantially 0 mm. The plasma processing was performed for apredetermined period of time. Then, it was checked whether or not adischarge mark was formed on the backside of the wafer W. The processingconditions were the same as those in the test example 1.

A result thereof is shown in FIG. 8. As can be seen from FIG. 8, in thecomparative example 1 (gap CL1<gap CL2), the abnormal discharge occurredon the backside of the wafer W. On the other hand, in the test examples1 and 2 (gap CL1>gap CL2), the abnormal discharge did not occur on thebackside of the wafer W. This indicates that the occurrence of theabnormal discharge can be effectively prevented by setting the gap CL2to be smaller than the gap CL1.

While the disclosure has been shown and described with respect to theembodiments, it will be understood by those skilled in the art thatvarious changes and modifications may be made without departing from thescope of the disclosure as defined in the following claims.

What is claimed is:
 1. A mounting table to which a voltage is applied,comprising: an electrostatic chuck having a mounting surface formounting a target object and a rear surface opposite to the mountingsurface, the electrostatic chuck having a first through-hole formed inthe mounting surface; a base, which is in contact with the rear surfaceof the electrostatic chuck, having a second through-hole communicatingwith the first through-hole; a cylindrical spacer inserted in the secondthrough-hole; and a pin accommodated in the first through-hole and thespacer, wherein gaps are formed between the pin and inner walls of thefirst through-hole and the spacer, and the gap between the firstthrough-hole and the pin is greater than the gap between the spacer andthe pin.
 2. A mounting table to which a voltage is applied, comprising:an electrostatic chuck having a mounting surface for mounting a targetobject and a rear surface opposite to the mounting surface, having afirst through-hole formed in the mounting surface; a base, which is incontact with the rear surface of the electrostatic chuck, having asecond through-hole communicating with the first through-hole; and a pinaccommodated in the first through-hole and the second through-hole,wherein gaps are formed between the pin and inner walls of the firstthrough-hole and the second through-hole, and the gap between the firstthrough-hole and the pin is greater than the gap between the secondthrough-hole and the pin.
 3. The mounting table of claim 1, wherein theelectrostatic chuck is made of ceramic and has therein an electrode, andthe base is made of a metal.
 4. The mounting table of claim 2, whereinthe electrostatic chuck is made of ceramic and has therein an electrode,and the base is made of a metal.
 5. The mounting table of claim 1,wherein the first through-hole is a gas hole for supplying a cold heattransfer gas.
 6. The mounting table of claim 2, wherein the firstthrough-hole is a gas hole for supplying a cold heat transfer gas. 7.The mounting table of claim 1, wherein the pin is a lifter pin forraising the target object from the mounting table, and the firstthrough-hole is a pin through-hole.
 8. The mounting table of claim 2,wherein the pin is a lifter pin for raising the target object from themounting table, and the first through-hole is a pin through-hole.
 9. Themounting table of claim 1, wherein on the assumption that a length ofthe gap in the first through-hole is g1; a thermal expansion coefficientof the base is α1; a thermal expansion coefficient of the electrostaticchuck is α2; a distance from a center of the mounting surface to acenter of the first through-hole is R; a diameter of the pin is D; adiameter of the second through-hole is d2; and a difference between atarget temperature and a reference temperature that is a temperaturemeasured when the first through-hole and the second through-hole arecoaxially disposed, the length g1 of the gap in the first through-holesatisfies a relation of g1≥(2·(R·(α1−α2)·ΔT+D)−d2−D)/2
 10. The mountingtable of claim 2, wherein on the assumption that a length of the gap inthe first through-hole is g1; a thermal expansion coefficient of thebase is α1; a thermal expansion coefficient of the electrostatic chuckis α2; a distance from a center of the mounting surface to a center ofthe first through-hole is R; a diameter of the pin is D; a diameter ofthe second through-hole is d2; and a difference between a targettemperature and a reference temperature that is a temperature measuredwhen the first through-hole and the second through-hole are coaxiallydisposed, the length g1 of the gap in the first through-hole satisfies arelation of g1≥(2·(R·(α1−α2)·ΔT+D)−d2−D)/2
 11. A plasma processingapparatus comprising: a processing chamber defining a processing spacewhere a plasma is generated; a gas supply unit configured to supply aprocessing gas into the processing space; and a mounting table providedin the processing space and configured to mount thereon a target object,wherein the mounting table to which a voltage is applied includes: anelectrostatic chuck having a mounting surface for mounting a targetobject and a rear surface opposite to the mounting surface, theelectrostatic chuck having a first through-hole formed in the mountingsurface; a base, which is in contact with the rear surface of theelectrostatic chuck, having a second through-hole communicating with thefirst through-hole; a cylindrical spacer inserted in the secondthrough-hole; and a pin accommodated in the first through-hole and thespacer, wherein gaps are formed between the pin and inner walls of thefirst through-hole and the spacer, and the gap between the firstthrough-hole and the pin is greater than the gap between the spacer andthe pin.
 12. A plasma processing apparatus comprising: a processingchamber defining a processing space where a plasma is generated; a gassupply unit configured to supply a processing gas into the processingspace; and a mounting table provided in the processing space andconfigured to mount thereon a target object, wherein the mounting tableto which a voltage is applied includes: an electrostatic chuck having amounting surface for mounting a target object and a rear surfaceopposite to the mounting surface, the electrostatic chuck having a firstthrough-hole formed in the mounting surface; a base, which is in contactwith the rear surface of the electrostatic chuck, having a secondthrough-hole communicating with the first through-hole; and a pinaccommodated in the first through-hole and the second through-hole,wherein gaps are formed between the pin and inner walls of the firstthrough-hole and the second through-hole, and the gap between the firstthrough-hole and the pin is greater than the gap between the secondthrough-hole and the pin.